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To combat the challenges that Material Scientists often face in the development of metallic nanofoams, Researchers from the University of California Davis have developed a new method that eliminates the potential occurrence of the adverse effects associated with typical production techniques.
Uses of Palladium
Palladium (Pd) is a lustrous and very rare metal that has been utilized in various applications including dental fillings and crowns, catalytic convertors, different electronics such as laptop computers and cellular phones, as well as an ideal catalyst for hydrogenation and dehydrogenation chemical reactions1. The catalytic property of Pd has also provided a useful solution to numerous energy storage devices including battery packs, power supplies and much more.
As the trend of reducing bulk materials to the nanoscale continues to show prosperous results in almost every applied industry, the use of Pd nanoparticles and nanostructures has shown a promising potential for enhancing current energy systems.
Metallic Nanofoams: Advantages and Limitations
Originally introduced about 20 years ago, metallic nanofoams are strong, lightweight and highly porous structures that exhibit a particularly high thermal and electrical conductivity that is useful for energy storage systems. The development of palladium nanofoams in the past has provided suitable materials use for organic chemical synthesis, hydrogen storage, fuel cells, batteries and even potential pollution control.
Traditional manufacturing techniques to produce these metallic foams are not ideal, as they often leave the product highly susceptible to contamination and poor crystallinity, both of which will ultimately affect their ability to function properly.
Freeze-Dry Manufacturing Technique
A recent study published in The Chemistry of Materials by a group of Researchers at the University of California Davis, College of Letters and Science has successfully fabricated palladium nanowire foams through a cross-linking and freeze-drying technique that appears ideal for hydrogen storage applications. After fabrication of polycrystalline Pd nanowires was completed by electrodeposition, confirmation of the porosity of the material was confirmed by transmission electron microscopy (TEM). The nanowires were then suspended in an ideal water level, and eventually sonicated to develop a randomly dispersed slurry mixture2.
The Researchers then placed this completely immersed slurry mixture in liquid nitrogen, thereby freezing the wires. The frozen Pd nanowires were then placed in a vacuum for 12 hours, removing the interstitial ice and purifying the final Pd nanowire foam of interest that exhibited a density of only 0.1%-1% of bulk Pd.
Testing the Nanowires for Hydrogen Storage Potential
To fully determine the potential of the Pd nanowire foam to adequately store hydrogen energy for future use, the Researchers exposed the wires to approximately 200 kPa of hydrogen for one hour. The study demonstrated that the hydrogen successfully penetrated the entire Pd nanowire in a uniform manner. While scanning electron microscopy (SEM) micrographs of the nanowire found that fractures developed within the material, most likely as a result of the strain posed during hydrogenation processes.
The Researchers believe this effect can be alleviated in future research endeavors. Additionally, the Pd nanowire foam was found to exhibit superior thermodynamic stability under high temperature and pressure processing, which was confirmed through calorimetric measurements during hydrogenation processes.
Looking Forward
The Pd nanowire foam produced in this study not only exhibited each of the highly attractive characteristics that are sought after when developing hydrogen storage systems, but also demonstrated a new and improved way to produce these types of highly complex materials. Future applications of this technique for other metallic nanofoam compounds could have beneficial effects for a wide variety of industrial applications.
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References:
- “Palladium”– Royal Society of Chemistry
- “Tunable Low Density Palladium Nanowire Foams” D. Gilbert, E. Burks, et al. Chemistry of Materials. (2017). DOI: 10.1021/acs.chemmater.7b03978.
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